I still haven't confirmed anything on my truck. I am getting ready to pull the engine and find out what it is since it is getting worse. I have taken the truck to another mechanic and he said rod bearing. Since I added STP it did quiten the knock down a little when holding the rpm's at around 2500, so I am about convinced it is a rod bearing. When I know for sure I will post.

When my timing chain was loose I had an knock just like you are describing (Different than what I got now). I used the stethoscope and could hear it plainly when I put the probe on the exhuast pipe. But after further probing around I put the end of the probe on the back section of the timing chain cover near the oil pan and I could actually feel the rattle. I put a comp cams double roller on it and the rattle went away for a while, but then came back. The comp cams chain was not much tighter than the one I just replaced. So I tore it down again and added a tensioner. The knock went way. But since I have developed this new problem I tore into it again to check it. I removed the tensioner from the comp cams chain and it was extremely loose (without the tensioner installed). What I did this time I bought a Cloyes double roller and put it on without the tensioner and It was a lot better fit. The tensioner probably works okay with the factory chain, but it seemed too tight with a double roller.